The present invention relates to a structurally mistuned array of flow directing elements, such as a row of rotor blades, to be used in turbomachinery for reducing the vibration which occurs in stator vanes used in the turbomachinery and for reducing the susceptibility of the flow directing element assembly to the tuned absorbed phenomenon.
Turbomachinery blades and vanes arranged in alternating rows are subject to destructive vibrations due to the aerodynamic action with other blade rows which rotate relative thereto. Still further, the rotor blades in a row can vibrate when spun through flow distortions caused by stator vanes in an adjacent or nearby row. Additionally, the rotating flow distortions due to the rotor blades cause stator vanes in an adjacent or nearby row to vibrate.
Changing the count of stator vanes in 180 degree segments, e.g. 40 stator vanes in a top segment and 42 stator vanes in a bottom segment, reduces the vibration of adjacent rotor blades. This is because the different circumferential spacings of the stator vanes cause the rotor blades to vibrate at two different frequencies during each rotor revolution. In a similar manner, changing rotor blade count will reduce stator vibration.
Vibrating rotor blades are susceptible to a detrimental phenomenon known as xe2x80x9ctuned absorbedxe2x80x9d or xe2x80x9cmode localizationxe2x80x9d. This phenomenon causes the vibration energy of an entire rotor assembly to become concentrated in just a few of the blades or flow directing elements in the rotor, leading to high vibration and premature failure of these blades or flow directing elements. One factor that contributes to this phenomenon is the structural coupling, through the rotor disk, between blades with similar natural frequencies.
Accordingly, it is an object of the present invention to provide an improved flow directing element array for use in turbomachinery.
It is a further object of the present invention to provide an improved flow directing element array as above which reduces the vibration of stator vanes in the turbomachinery.
It is yet a further object of the present invention to provide an improved flow directing element array as above which reduces the susceptibility of a rotor to the tuned absorbed phenomenon.
The foregoing objects are attained by the flow directing element array of the present invention.
In accordance with the present invention, an array of flow directing elements known as a blade row for use in turbomachinery is provided. The array broadly comprises a plurality of flow directing elements mounted to a disk and extending about the disk in a circular pattern having four quadrants. Each flow directing element in a first one and a second one of the quadrants preferably has a greater mass than each flow directing element in a third one and a fourth one of the quadrants with each of the first and second quadrants being located intermediate the third and fourth quadrants. The flow directing elements are further arranged so that the number of flow directing elements in each of the first and second quadrants is less than the number of flow directing elements in each of the third and fourth quadrants.
As used herein, the word turbomachinery refers to devices, such as gas turbine engines and steam turbines, which operate by exchanging energy with a working fluid using alternating rows of rotating blades and non-rotating vanes or stators.
Other details of the flow directing element array of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawing(s) wherein like reference numerals depict like elements.